Behind the Picture: Photos From the Night Marilyn Sang to JFK, 1962

Fifty-plus years ago, on a spring night in New York City, 35-year-old Marilyn Monroe -- sewn into a sparkling, jaw-droppingly tight dress -- stood alone in a spotlight on a dark stage. She took a breath, began to sing -- and 15,000 men and women who filled the old Madison Square Garden that night knew, simply knew, that they were seeing and hearing something that they would never, ever forget.

The song, of course, was "Happy Birthday," and Marilyn's breathy, intimate rendition — sung, as if the two of them were utterly alone, to President John F. Kennedy — has been celebrated, analyzed and lovingly parodied countless times in the five decades since that indelible performance. But beyond the buzz that Marilyn's "Happy Birthday" generated — including, of course, tossing fuel on the already smoldering rumors about an affair between the movie star and the president — the moment, captured from above by photographer Bill Ray in his iconic picture of Monroe, played a key role in the legends that eventually grew around both the actress and JFK. Marilyn, after all, died less than three months later; Kennedy was assassinated the following fall. For stargazers and dusty old historians alike, the night that Marilyn sang to JFK remains an uncanny, once-in-a-lifetime collision of sex, politics, power and pop culture.

[WATCH: Bill Ray discusses how he got his famous shot of Marilyn.]

"For most people my age," remembers Ray, who was 26 in 1962, "Kennedy was something of a god. We were so relieved to have a young, good-looking person in the White House after Eisenhower."

Of the setup for the birthday gala that night in the Garden, Ray recalls that "all of the photographers were in front in the beginning of the show, but it was another one of these events where security says, 'Hey, we're really glad you came. Take a few pictures — and get your ass out!' The Secret Service started clearing everybody out after a few shots. I was afraid of being held in a cattle pen with the rest of the photographers, so I got away and started moving around the Garden on my own."

Trying to find an angle from which he might be able to get both Marilyn and JFK in the same frame, Ray moved higher and higher up in the Garden. He had made his way on to a catwalk, literally up among the building's girders, when the moment that would forever define the evening suddenly arrived.

"It had been a noisy night, a very 'rah rah rah' kind of atmosphere," Ray told LIFE.com. "Then boom, on comes this spotlight. There was no sound. No sound at all. It was like we were in outer space." Marilyn was onstage, taking off a white fur to reveal that utterly gorgeous, scandalous dress underneath. "It was skin-colored, and it was skin-tight. It was sewn on, covered with brilliant crystals. There was this long, long pause . . . and finally, she comes out with this unbelievably breathy, 'Happy biiiiirthday to youuuu,' and everybody just went into a swoon. I was praying [that I could get the shot] because I had to guess at the exposure. It was a very long lens, and I had no tripod, so I had to rest the lens itself on the railing, and tried very, very hard not to breathe."

Here, on what would have been JFK's 97th birthday, LIFE.com presents Bill Ray's unforgettable picture of Marilyn, alone in the spotlight, along with many more photos from the president's birthday gala at the Garden that were not published in LIFE magazine.